An image processing apparatus which clips an image of a document region from image data obtained by reading a document has been known. FIG. 1 is a schematic view showing image data obtained by reading a document. The image data 100 include a document region 101 formed from a set of pixels obtained by reading an image of a document with an imaging device, and a background region 102 formed from a set of pixels obtained by detecting the light outside the document with the imaging device. In order to clip an image of the document region, edge points 104 on the boundary line 103 between the document region 101 and the background region 102 are detected. In FIG. 1, each “X” mark denotes different edge point 104 on the boundary line 103.
As a technology for detecting a terminal portion of a document, an image reading apparatus has been known which cancels noise in the terminal portion of the document by determining a specific region as the terminal portion of the document based on shading data, and replacing the value in the specific region of image data with a prescribed value. A mask correction circuit of the image reading apparatus determines a specific region as a terminal portion of the document on image data inputted from a gamma correction circuit based on the shading data to be utilized for performing shading correction. The value of the image data determined as the specific region is converted with a prescribed value and is outputted to each circuit in later stage.
An image reading apparatus which suppresses density difference among respective elements of a line sensor. This image reading apparatus includes a line sensor having photo detectors arrayed along a prescribed direction, and a white reference plate provided in a second read-out area, among read-out areas of the line sensor, i.e., is other than a first read-out area for reading-out an image recorded at least on a recording medium. The image reading apparatus also includes correction means for correcting the pixel value in the first read-out area read by a first photo detector corresponding to the first read-out area, based on the pixel value of the second read-out area read by a second photo detector corresponding to the second read-out area.
Related art is disclosed in Japanese Laid-open Patent Publications No. 2009-260893 and 2007-19853.